Chamberlin and Boyce's first attempt of a relational database language was Square, but it was difficult to use due to subscript notation. After testing SQL at customer test sites to determine the usefulness and practicality of the system, IBM began developing commercial products based on their System R prototype including System/38, SQL/DS, and DB2, which were commercially available in 1979, 1981, and 1983, respectively.After moving to the San Jose Research Laboratory in 1973, they began work on SEQUEL. (now Oracle Corporation) saw the potential of the concepts described by Codd, Chamberlin, and Boyce, and developed their own SQL-based RDBMS with aspirations of selling it to the U. SQL deviates in several ways from its theoretical foundation, the relational model and its tuple calculus.
Since then, the standard has been revised to include a larger set of features. introduced the first commercially available implementation of SQL, Oracle V2 (Version2) for VAX computers.
SQL is a set-based, declarative programming language, not an imperative programming language like C or BASIC.
However, extensions to Standard SQL add procedural programming language functionality, such as control-of-flow constructs.
Despite the existence of such standards, most SQL code is not completely portable among different database systems without adjustments. By the year 1986, ANSI and ISO standard groups officially adopted the standard "Database Language SQL" language definition.
This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasi-relational database management system, System R, which a group at IBM San Jose Research Laboratory had developed during the 1970s. New versions of the standard were published in 1996, 1999, 2003, 2006, 2008, 2011, and most recently, 2016.